The present invention refers to the extraction of parallelepiped shaped blocks of rock from a rock formation and to an extractor to be used for such purpose.
The extraction of ornamental blocks of rock from rock formations, especially of granite, began to show signs of advancement in recent years with the development of specific explosives. Such explosives are placed in drill holes aligned along one or more cutting planes and then detonated simultaneously so as to make extraction more rapid.
FIGS. 1 to 4 of the accompanying drawings illustrate the most common method presently used for the extraction of blocks of rock from solid rock formations. Fundamentally, it comprises the following steps:
Step 1: as shown in FIG. 1, a large block of rock having, for example, a volume of 100 to 400 cubic meters is freed from the rock formation. Slots or channels are opened along the sides of the block of rock to be removed so as to relieve internal stresses. The slots or channels are normally opened by means of jet flame burners or slot-drills forming secant perforations.
Rear, vertical and/or horizontal perforations are then drilled and the rock block is separated by the simultaneous detonation of explosives placed in such perforations.
One manner of carrying out this method is to take advantage of the natural separations found in many rock formations. In order to extract the block, it is sufficient to drill the spaced aligned perforations suitably arranged in a plane normal to the plane defined by the natural separation in the rock formation and then to detonate the explosives placed in such perforations.
Another manner is not to make the vertical perforations, but rather to open a rear slot or channel and to drill perforations in the plane of the natural separation, then simultaneously detonating the explosives placed in such perforations.
Stage 2: as shown in FIG. 2, in this step the block of rock is sub-divided along the planes of separation defined by corresponding aligned drillings, separation being obtained by means of explosives or metal plugs driven into the drillings so as to produce smaller blocks of rock of commercial size.
Stage 3: as shown in FIG. 3, this stage concerns the finishing of the block of rock by squaring it perfectly using closely spaced aligned drillings, the block being cut by means of plugs driven into the drillings or alternatively cutting is effected by means of manual tools. Only then will the block be in condition for being passed for final processing in rock slicing machines.
The following problems in the above method are to be noted:
low yield. When explosives are used, the block does not always separate from the rock formation in the manner intended, be it due to lack of precision in the calculations for the explosive, be it due to a misalignment of the rear perforations with respect to the cutting plane; PA1 since the vertical and horizontal perforations are normally deep, it is necessary, as shown in FIG. 4, to provide for an angle greater than 90.degree. between the planes formed therebetween so as to avoid jamming of the separated block. This makes it necessary to square the block of rock later which means loss of material and additional finishing work. PA1 a) cutting into the surface of the rock formation a slot having a depth substantially equal to a width dimension of said blocks; PA1 b) drilling into said surface of the rock formation a first series of parallel aligned perforations orthogonal to said slot, said perforations terminating along the bottom of said slot and defining a first cutting surface orthogonal to the plane of said slot; PA1 c) drilling into said surface of the rock formation a plurality of parallel second series of parallel aligned perforations, said perforations of each of said second series defining a second cutting surface orthogonal to the plane of said slot and to said first cutting surface; PA1 d) separating by the use of plugs applied in the perforations of said first and second series, the blocks defined by steps a) to c); and PA1 e) carrying out steps a) to d) repeatedly so the slot of step a) is cut from the exposed surface of the rock formation, beginning along a line defined by the outer ends of the perforations of said first series of perforations, whereby the exposed surface of the rock formation, after extraction of the various blocks in steps d), acquires a stepped profile. PA1 a) cutting orthogonally into a first surface of one step of said stepped profile a slot of a depth equal to that of the second surface of the same step, said slot being cut slightly above the plane of the second surface of the immediately previous step; PA1 b) cutting orthogonally into the second surface of the same step a first series of parallel aligned perforations along the junction between said second surface of the same step and the first surface of the immediately following step, the perforations of the first series extending to the bottom of said slot; PA1 c) cutting orthogonally into the second surface of the same step a plurality of parallel second series of parallel aligned perforations extending to said slot, said second series defining lines normal to said junction; PA1 d) separating by the use of plugs applied in the perforations of said first, and second series, the blocks defined by steps a) to c); and PA1 e) repeating steps a) to d) with respect to the following steps of the profile of said rock formation, extracting the respective blocks of rock.
The purpose of the present invention is to overcome the majority of the above problems by means of a process that permits the extraction of effectively already finished blocks that do not have the cracks or microfissures that usually appear when conventional processes are used, thus ensuring an improved yield with less labour.
A further object of the present invention is to provide an extractor of blocks of rock for carrying out the process.